This invention relates to an apparatus for solder joining metal tapes in a continuous tape laminating apparatus.
Soldering has been defined as metal coalescence below about 800.degree. F. As a result, soldering facilitates joining parts while minimizing damage from heating. Solder alloys are comprised of tin and lead, and the tin component reacts with metals to be joined to form a metallurgical bond. In many soldering systems, an intermetallic compound is developed at the interface between the solder and the base metal, producing an essentially complete metallurgical joint. The cleanliness and chemical composition of the surfaces to be joined are critical to the process. For example, flux can be used to insure that the base metal is sufficiently cleaned to provide adequate spread and flow of the soldering alloy to promote joint formation. However, when a flux is not used surface cleanliness, e.g., freedom from surface oxides, is critical to joint formation.
One application that has been disclosed for solder joined metal tapes is for laminated superconducting tapes, for example disclosed in U.S. Pat. No. 3,537,827. Briefly described, the laminated superconducting tape is comprised of a brittle triniobium tin superconducting layer bonded between outer laminae of non-superconductive metals having a coefficient of thermal expansion greater than that of the triniobium tin inner layer. The outer laminae are bonded integrally to each side of the triniobium tin inner layer by soldering. As a result, the triniobium tin inner layer is in a state of mechanical compression which results from the fact that the outer laminae are in a state of mechanical tension.
Uniform solder joining of the outer laminae to the relatively brittle inner layer provides benefits, such as, improved thermal conductivity for cooling of the superconducting core of the tape, improved formability of the tape, and greater resistance to handling damage. For some applications the laminated tape must have a uniform cross section, for example to enable uniform winding of the tape to form coils. Therefore, it is desirable to solder the metal tapes to form a uniform solder joint, and a laminated tape having a uniform cross-section with a smooth surface finish in a continuous operation. However, imperfections in the tapes that are to be laminated such as camber or wavy edge cause misalignment of the tapes in the width dimension, oxidized tape surface causes dewetting and poor solder bonding, and particles in the solder such as dross (tin oxide) or intermetallic compounds (CuSn) can cause non-uniform cross-sections and excessively rough surface finish defects in the laminated tape.
Excessive time at the soldering temperature, about 250.degree. C., can produce softening of the outer laminate. Since yielding of the outer laminate will cause fracture of the relatively brittle superconductive inner laminate, it is desirable to maintain the yield strength of the outer laminate as high as possible. Therefore it is desirable to minimize the time the tapes are at the soldering temperature.
It is an object of this invention to provide an apparatus for solder joining metal tapes to form a laminated metal tape.
It is another object of this invention to provide an apparatus for solder joining metal tapes symmetrically aligned in the width dimension.
It is another object of this invention to provide an apparatus that aligns metal tapes symmetrically in the width dimension having nonuniformities that cause misalignment of the tapes such as camber or wavy edge.
It is another object of this invention to provide an apparatus for solder joining metal tapes rapidly so that the outer laminae is at the soldering temperature for a minimum time to reduce softening of the outer laminae.
It is another object of this invention to form an apparatus for solder joining metal tapes with a high uniformity of solder bonding across the entire surface of the facing tapes.
It is another object of this invention to provide an apparatus for continuously solder joining metal tapes while minimizing bending or abrasion of the tape surface.
It is another object of this invention to provide an apparatus for continuously solder joining metal tapes.